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In this article, the optimum stacking sequence with maximum buckling load factor of a plate made of M91/IM10 unidirectional prepreg material, which has a very high strength compared to the materials used in the aerospace industry, is obtained by genetic algorithm method. The composite plate in question is simply supported at 4 edges and subjected to biaxial in-plane compressive loads. With the computer code developed using the genetic algorithm method, stacking sequences that provide maximum buckling strength at certain fiber angle ranges and certain number of layers for various load cases and various plate aspect ratio combinations are obtained. The laminate is assumed to be symmetrical and balanced. The results are compared with the results obtained from graphite/epoxy composite material, which has been studied in the literature. The comparison reveals that a plate made of M91/IM10 prepreg material can provide the same buckling performance with lighter structures than graphite epoxy. [ABSTRACT FROM AUTHOR]

In this article, the buckling of carbon nanotube (CNT) patterned cylindrical shells subjected to axial compressive load is presented within the framework of shear deformation theory (SDT). The material properties of nanocomposites change as a linear function depending on the thickness coordinate. The basic equations of cylindrical shells with CNT pattern are derived based on Donnell type shell theory and the critical axial load expression is obtained within the framework of SDT by applying Galerkin method. The effects of transverse shear deformations on the critical axial load of functionally graded CNT patterned cylindrical shells are investigated by changing CNT patterns, volume fraction ratio and shell parameters. [ABSTRACT FROM AUTHOR]

In this study, free vibration and buckling analyses of functionally graded (FGM) sandwich beams is investigated by Navier's method. Displacement field is defined according to the first order shear deformation theory, and the equations of motion are derived by the Lagrange's principle. Volumetric ceramic ratio is defined by a power-law rule. In the analytical solution, different trigonometric series functions are used for each end conditions considered. Two cases of functionally graded sandwich beams are considered: a) Homogeneous ceramic core and FGM faces (Type A), and b) FGM core and homogeneous faces (Type B). Natural frequencies and buckling loads are obtained for different boundary conditions, power-law indices and slenderness. Numerical results are compared with the available literature, and a good agreement are obtained between the results. [ABSTRACT FROM AUTHOR]

Cylindrical steel tanks are widely used to store variety liquids such as water, petroleum, and industrial chemicals. They also have been becoming widespread for cooling in nuclear power plants last years. Steel liquid tanks can be exposed during earthquakes and also they can cause great financial and environmental damage with their containing petroleum or other hazardous chemical liquid. The natural vibration periods of these tanks, which are important engineering works, are in the range of 0,1 s - 0,5 s. If there is no mechanism to absorption the maximum earthquake energy that occurs in this short period, the tank will resonate and damage will occur. For this study, deformations in cylindrical steel tanks were used for earthquake recording of 0.22 seconds since buckling occurred in a very short period. In addition, this time and earthquake values are ideal for nonlinear analysis because ANSYS Workbench "Explicit Dynamics" tool provides very good results in the dynamic analysis of structures under destructive and short-term forces. In order to provide the interaction between the water and the tank wall, the "Eulerian Body" mesh technique is preferred in "Explicit Dynamics" model. In the analysis, an open-top tank model, a conical model and a torisperical closed model were used and the analyzes were repeated for three different tank wall thicknesses. Depending on the shell thickness of the tank and the shape of the tank roof, the causes of deformation and buckling were examined. As a result of the analysis, it was seen that torispherical closing of the cylindrical steel liquid tanks reduced deformation and buckling. [ABSTRACT FROM AUTHOR]

In this study, the thermal buckling analysis of the non-homogenous shallow spherical shell is investigated. Firstly, the analytical modeling of non-homogenous material properties and appropriate thermal expansion coefficient which vary continuously through the thickness direction is made. In the formulation of the problem, Kirchhoff-Love's first order shell theory is used and Hooke's law is taken into account for stress-strain relations. By using Donnell-Mushtari-Vlasov's (DMV) assumptions and linear stress-displacement relation, the stability equations depending on three displacements are obtained. Stability equations are solved for the simply supported boundary condition and analytical expression for the dimensionless critical uniform temperature rise is found. In numerical computations, the effects of variations of the elasticity modulus and appropriate thermal expansion coefficient as a power function according to thickness direction and variation of the geometric parameters of the sphere on the critical uniform temperature rises are examined as. To test the validity of this study, the obtained results are compared with counterparts in the open literature. [ABSTRACT FROM AUTHOR]

Displacements take considerable values as the thicknesses of the cross-sections of box girder bridges decrease. Because of that reason, second order effects need to be taken into account in order to make an accurate analysis. In this study, application fields of a rectangular and a curved shell finite element are extended by adding second order effects to the formulations. Mass matrices of these elements are obtained to find the natural vibration periods of straight and curved axis box girder bridges, open section bridges and circular plates. For the analysis of box girder bridges with cross-sectional diaphragms, membrane finite elements can be used in order to define the cross-sectional diaphragm effect. For this purpose, the formulation of a general quadrilateral membrane finite element is given and the mass matrix of the element is obtained to be used in dynamic analysis. Both rectangular and curved shell finite elements which are used here have seven degrees of freedom per node. General quadrilateral membrane finite element which is selected to be used as cross-sectional diaphragms has three degrees of freedom per node which are two translations and one inplane rotation and its formulation is based on displacement superposition. Stiffness and mass matrices of the rectangular shell finite element are obtained by using closed form formulation while Gauss integration rule is used for the stiffness and mass matrices of curved shell and quadrilateral membrane finite elements. The analysis of box girder bridges using matrix displacement method is described and determination of buckling loads and natural vibration periods of the systems are explained briefly. The part of the bridge between two cross-sections composed of a number of finite elements is called a macro-element. Stiffness, loading and mass matrices are established independently for different macro-elements and system stiffness, loading and mass matrices are obtained by the combination of these matrices. Three examples are given in order to illustrate the work done in this study. In the first example, a circular plate is solved for fixed and clamped support conditions and buckling loads are obtained for both cases. The results are close to the results of analytical solution and the buckling load of the clamped circular plate is found to be 3.5 times of the buckling load of the circular plate with fixed supports. The second example is a reinforced concrete box girder bridge with straight axis. It is solved according to the first and the second order theories under its own weight and vertical displacements of the midspan are compared with each other. It is seen that the increment of the vertical displacements is only about 1% which is because the thicknesses of the cross-section are not considerably small. It can be said that the increment ratio increases as the thicknesses decrease. Then, the same problem is considered to have two cross-sectional diaphragms at the support cross-sections and four diaphragms, two at the supports and two at the span cross-sections. It is solved under antimetric vertical point loads subjected at the midspan and vertical displacements and inner forces are compared with each other. It is concluded that adding diaphragms decreases both vertical displacements and inner forces due to warping. Also, the first four natural vibration periods of the bridge with and without cross-sectional diaphragms are obtained and it is observed that natural periods of the system decrease by the usage of diaphragms. A curved reinforced concrete box girder bridge which is the last example, is solved under its own weight according to the first and the second order theories and first four natural vibration periods are obtained.The increment of the vertical displacements of the midspan cross-section is about 1%. The conclusions obtained are as follows: Buckling loads of circular plates are close to the values which are obtained analytically. Second order effects are not considerable for reinforced concrete box-girder bridges because of their cross-sectional thicknesses. Cross-sectional diaphragms reduce the vertical displacements and inner forces of the bridge due to warping. Natural vibration periods of box-girder bridges decrease by the usage of cross-sectional diaphragms [ABSTRACT FROM AUTHOR]

In the study, two and three-dimensional bending, buckling, and free vibration analysis of homogenous and isotropic rectangular plates are made by the method of differential quadrature. The weighting coefficients for differential quadrature are obtained using the power, Chebyshev and Lagrange polynomials. The governing differential equations (constitutive equations and boundary conditions) are reduced to a linear algebraic equations or a standard eigenvalue equation in terms of the unknown function values at the grid points in the field domain via differential quadrature method. The obtained results are then compared with the other results in the related literature. It is found that the obtained results are suitable in point of view the engineering analysis concept. [ABSTRACT FROM AUTHOR]